So far disclosed as compounds obtainable by the ring opening reaction of tetrafluorooxetane are 2,2-difluoropropionic acid derivatives represented by XCH2CF2COY (wherein X is R1O— or R2CH2CF2CF2O— in which R1 and R2 each is a saturated aliphatic group or halogenated saturated aliphatic group containing 1 to 3 carbon atoms, for instance; and Y is —OR3 in which R3 is a saturated aliphatic group or halogenated saturated aliphatic group containing 1 to 3 carbon atoms, for instance (cf. e.g. Patent Document 1).
However, no carboxylic acid salts are known as compounds obtainable by the ring-opening reaction of tetrafluorooxetane. It is also unknown whether tetrafluorooxetane-derived ring-opening reaction products can be used as surfactants.
Partially fluorinated compounds represented by Rf—(CH2)m—Rf′—COOM (in which m is 1 to 3, Rf is a perfluoroalkyl or perfluoroalkoxy group containing 3 to 8 carbon atoms, Rf′ is a straight or branched perfluoroalkylene group containing 1 to 4 carbon atoms and M is NH4, Li, Na, K or H) are known as surfactants useful in polymerizing fluorinated monomers (cf. e.g. Patent Document 2). In this document, however, there is no description or suggestion about the extents of the reduction in surface tension as brought about by such surfactants or the mean primary particle sizes of the polymers obtained by using the surfactants.                Patent Document 1: Japanese Kokai Publication H02-223538 (Claim 1)        Patent Document 2: Japanese Kokai Publication H10-212261        